&
FACT
D
ATA
SHEET
presented by
There seems to be a lot of misinforma-
tion regarding performance and efficien-
cy of Staple-Up™ systems. Despite the
fact that Watts Radiant has experience
with tens-of-thousands of S
taple-Up
systems over the last 22 years in some
of the coldest climates in the country,
some insist that Staple-Up "doesn't
work" or it has "limited heat capacity"
or it is "much more expensive to oper-
ate."
The goal of this technical piece is to put
these myths to rest and help explain the
advantages of Staple-Up systems.
Question:
Is it true an Onix S
taple-Up application
costs less than PEX
, even though the
Onix tubing costs more?
Answer:
Yes, Onix Staple-Up applications do
cost less than PEX Underfloor applica-
tions. There are two main reasons. The
first has to do with labor. Onix installs
2-3 times faster
than PEX. This is due
in part to the increased flexibility of
Onix over PEX, not to mention the
additional time needed to install the spe-
cial fasteners required for PEX, such as
clips and/or heat transfer plates.
These additional fas-
teners also increase
the cost of a PEX sys-
tem. Even though
Onix tubing may cost
more than PEX tub-
ing, the cost of Onix
with staples is about
40% less than PEX
with metal plates (see
table).
Question:
Why can't PEX be stapled directly to the
underside of the subfloor like Onix?
Answer:
PEX will expand and contract as it is
heated and cooled. How much it will
move is directly proportional to the
change in temperature. PEX tubing
expands 1.1 inch for every 10 degree
rise in temperature for every 100 feet of
tubing. If a 200 ft. circuit of PEX is
filled with 60°F water and heated to
160°F, the PEX expands approximately
22 inches
.
This movement can cause noise and
wear, either against the floor or against
the staples themselves. A considerable
amount of noise can be generated as the
PEX expands and rubs against the metal
plates or staples. This noise is transmit-
ted into the house. Also, there is a ques-
tion of heat transfer. As the PEX
expands it has a tendency to pull away
WattsRadiant Literature, May 1, 2003 ©WattsRadiant 2003 page 1
Onix Staple-Up PEX w/Plates PEX Sandwich PEX Thinslab
Tubing Cost $2.55 $1.24 $1.24 $0.85
Staples/Screws $0.02 $0.50 $0.08
Metal Plates $4.00
SubRay $4.65
Light Crete $4.00
Structural $1.50
Modifications
TOTALS $2.57/sf $5.74/sf $5.97/sf $6.35/sf
Values shown are based on a list price per square foot basis. Cost considerations are for tubing and attachment materials only.
Labor costs are in addition to the totals listed above.
Staple–Up
™
With Onix
from the subfloor. This
separation decreases
the tubing's ability to
transfer energy to the
subfloor, and reduces
its overall heating abil-
ity.
Question:
Why doesn't Onix have
these problems?
Answer:
Onix is comprised of a
cross-linked EPDM
compound that does
not expand with tem-
perature changes. Onix
is the same diameter
and length at 200°F as
it is at 50°F
.
No expansion means
no wear on the tubing,
no noise and no
reduced heat transfer
due to tubing moving
away from the floor.
Question:
I've heard Staple-Up applications cause
thermal striping. Is this true?
Answer:
No. Onix Staple-Up does not cause ther-
mal striping (objectable temperature dif-
ferences). All radiant floor applications
will experience some thermal variances
in floor surface temperature on start up.
This is due to the instantaneous load on
the floor at that time. As the floor reach-
es steady-state conditions, this variance
evens out, resulting in a very even floor
temperature.
The surface temperature for an Onix
Staple-Up system will be nearly identi-
cal to that of a PEX underfloor system
with plates.
Most ThinSlab applications will experi-
ence a greater sense of thermal striping
on start up than a Staple-Up application.
This is because the increased conductiv-
ity of the thin concrete above the tubing
sends the heat to the surface faster than
the mid-point between the circuits. This
results in a greater initial striping.
Tube spacing has a direct impact on
how much temperature difference a
floor can experience. The wider the tube
spacing the greater the potential for
striping. Staple-Up applications are 8"
on center while Thin Slab applications
are usually 12" on center.
Phase 1: Initial Start-up Conditions
Radiant
Energy Transfer
Foil Faced Insulation
Air tight cavity is important to help maintain a constant,
uniform air temperature in the joist cavity.
Onix stapled directly to subfloor.
&
FACT
D
ATA
SHEET
WattsRadiant Literature, May 1, 2003 ©WattsRadiant 2003 page 2
Phase 2: Mid-Point Conditions
Phase 3: Steady-State Conditions
Conductive Energy Transfer
80°F
77°F
80°F
77°F
The two images on to the left show a the temperature of a floor in
a standard forced air heated home. The image to the right shows
a radiant tile floor.
Notice the color of the radiant floor and the person’s hand. Both
are about the same color, indicating both are about the same tem-
perature. The person in this room is losing very little energy to
the floor and is much more comfortable as a result.
Once all properly installed radiant sys-
tems reach steady-state conditions, tem-
perature differences are insignificant,
resulting in a very even floor tempera-
ture.
Question:
I've been told heat transfer plates are
required to spread the heat out across
the floor. Why doesn't Onix need heat
transfer plates?
Answer:
Onix does not need heat transfer plates
for two reasons. First, Onix is in direct
contact with the subfloor
, resulting in
direct conductive, efficient heat transfer.
Second, Watts Radiant recommends all
Onix S
taple-Up installations use foil-
faced insulation
. The foil on the insula-
tion "reflects" the downward energy
back up into the subfloor. This reflected
energy is spread out over the bottom of
the subfloor, creating an even tempera-
ture.
Question:
Does Onix Staple-Up take longer to
respond than other frame floor applica-
tions?
Answer:
No. Response times are dictated by the
thermal mass of the construction materi-
al, not the radiant tubing. All construc-
tion materials have a Specific Heat
Value; this is the amount of energy
required to raise the temperature of one
pound of material one degree
Fahrenheit.
The tables reflect the requirements for a
1,000 sf. room with a floor temperature
change from 50°F to 80°F with a 50,000
Btu/hr output boiler. These numbers
only reflect the time and load required
to change the floor mass temperature,
and do not take into account the addi-
tional load required to raise the room
temperature, or to sustain the room's
heat load.
&
FACT
D
ATA
SHEET
WattsRadiant Literature, May 1, 2003 ©WattsRadiant 2003 page 3
Onix Staple-Up Nomograph showing a supply temperature of 125° with a BTU load of 25 BTU/sqft and
floor surface temperature of 81°F.
PEX with Plates Nomograph showing a supply temperature of 120° with a BTU load of 25 BTU/sqft and
floor surface temperature of 81°F.
Question:
Why don't hanging PEX applications
work as well as Onix Staple-Up?
Answer:
Hanging PEX applications suspend the
tubing in the joist cavity with a series of
plastic clips spaced every 24 - 32" on
center. This is done to eliminate the
noise as the PEX tubing expands and
contracts with temperature changes
.
This creates an air gap between the
PEX tubing and the subfloor, eliminat-
ing conductive heat transfer from the
tubing. A major result of this lack of
contact is a reduction in the total BTUs
produced
. Most hanging PEX applica-
tions are limited to a maximum of 20
BTU/hr per square foot, often requiring
the installation of supplemental heat.
Onix Staple-Up applications can pro-
duce up to 45 BTU/hr/sq. ft. of useable
heat. This is a result of the Onix having
direct contact with the subfloor.
Question:
Why does Onix require a higher supply
water temperature than PEX when both
are installed the same way?
Answer:
Onix requires a slightly higher water
temperature because of the physical
properties of the material. Onix is com-
posed of EPDM rubber with a thicker
wall profile (added resistance to jobsite
abuse) than a PEX tubing.
Due to the thicker wall, a slightly higher
water temperature is required to achieve
the same outside tubing temperature as
would be seen with PEX. Since both
pipe outer surface temperatures are the
same, then they both have the same
BTU delivery to the floor and same
overall system response.
On the average, when compared to
PEX, Onix will only see around a 5-8°F
variance on supply fluid temperatures
.
Question:
Doesn't a higher supply temperature
mean higher operating costs?
Answer:
No. Operating costs are determined
solely by the amount of energy con
-
sumed (BTUs), not by the supply water
temperature.
One easy way to monitor energy usage
is to measure flow rate (gpm) and sys-
tem temperature drop (supply water
temp - return water temp). At a flow
rate of one gallon of pure water per
minute, a temperature drop of 20°F will
"deliver" 10,000 BTU/hr. Whether the
HiGuard™ Industrial Cover
AlumaShield™ Oxygen Barrier
Durel™ Inner Tubing
Aramid™ Fiber Reinforcing
Contour Extrusion Layer
Fluid Channel
Onix™ by Watts Radiant
Inside Diameter Outside Diameter Thermal Conductance Thermal Resistance
Tubing Material (inch) (inch) (Btu/hr.*ft.*°F) (hr.*ft.*°F/Btu)
1/2" EPDM 0.5 0.875 0.17 0.5239
1/2" PEX-AL-PEX 0.472 0.63 0.26 0.1767
1/2" PEX 0.472 0.63 0.237 0.1939
1/2" L Copper 0.545 0.625 223 0.9775 x 10
-4
Temperature Drop
Tubing Material (tw - td) °F
1/2" EPDM Rubber 13.098
1/2" PEX-AL-PEX 4.418
1/2" PEX 4.848
1/2" L Copper practically 0°F
&
FACT
D
ATA
SHEET
WattsRadiant Literature, May 1, 2003 ©WattsRadiant 2003 page 4
The average supply fluid temperature difference
between Onix and PEX is approximately 8°F.
tw = supply fluid temperature
td = outside tube surface temperature
Fluid Temperature Variances
Various Piping Thermal Properties
4” Concrete 9.80 BTU/ft
3
°F
1.5” Thin Slab 3.22 BTU/ft
3
°F
0.75” Subfloor (Staple-Up) 1.10 BTU/ft
3
°F
Heat Capacities
4” Concrete 294 MBH
1.5” Thin Slab 96.6 MBH
0.75” Subfloor (Staple-Up) 33.0 MBH
BTU’
s Required
4” Concrete 5.88 Hours
1.5” Thin Slab 1.93 Hours
0.75” Subfloor 0.66 Hours
Time Required to Heat Floor
&
FACT
D
ATA
SHEET
temperature drop is from 150°F to
130°F or 110°F to 90°F, one gpm will
always "deliver" 10,000 BTU/hr.
Btu/hr = GPM x 500 x DT
GPM = system flow rate in
gallons per minute
DT = Supply water temperature -
return water temperature
Most radiant systems operate with a
non-condensing boiler, meaning the
boiler needs to operate at 140°F to
160°F (supply) or above. So, whether a
radiant system operates at 150°F or
110°F, the boiler water is "mixed down"
to supply the radiant system. This
means the flue and stack losses from the
boiler will be the same for both radiant
supply temperatures.
Remembering that the ener
gy consumed
(BTU/hr.) is determined by flow rate
and temperature DROP (not supply tem-
perature), a radiant system that requires
150°F supply will not use more energy
that a system that requires 110°F.
The only time a lower water tempera-
ture translates to better efficiency is if a
condensing boiler is used. These boilers
are designed to operate at very low
return temperatures, such as a
snowmelting application.
Question:
What material is Onix made from?
How is it different from other rubbers
like automotive radiator hose or other
radiant hose materials?
Answer:
Onix is a multi-layer composite product,
with EPDM, aramid reinforcing and a
ductile aluminum oxygen barrier.
EPDM stands for Ethylene Propylene
Diene Monomer, which is a cross-linked
synthetic rubber. The peroxide-cured
carbon-carbon bonds that form the
cross-linking in the Onix tubing are
extremely stable and give Onix the abil-
ity to resist sunlight, oxidative aging,
and and long term effects of high tem-
perature operation.
Question:
What testing has taken place to ensure
Onix will last?
Answer:
Watts Radiant continuously tests Onix
in multiple phases of production. Each
batch of tubing produced is tested to a
min. 100 psig pressure to ensure burst
resistance. A Rheometer test is also per-
formed on each batch, which tests the
cross-linking. During production other
material properties are tested, such as
tensile strength, elongation, specific
gravity, and viscosity levels.
Besides being operated for over 60,000
continuous hours of testing at 180°F,
Watts Radiant sends samples of Onix to
independent labs for further testing.
These labs test the components used in
the construction of Onix tubing.
These tests determine the physical and
chemical changes the compenents
undergo. Based on the variances from
beginning to end, an estimated life span
is determined.
-
Question:
How does Onix compare to PEX?
Answer:
Onix outperforms PEX on several lev-
els.
1.Onix has a tighter bend radius
than
an equivalent PEX size, making
installation easier. Onix can be
installed in tighter areas, allowing
for more effective coverage.
WattsRadiant Literature, May 1, 2003 ©WattsRadiant 2003 page 5
Tensile Strength . . . . . . . . . . . . . . . . . . . .1000 psi
Percent Elongation . . . . . . . . . . . . . . . . . .300 %
Low Temp Flexibility . . . . . . . . . . . . . . . .10 times ID @ -40 Deg F
Ozone resistance . . . . . . . . . . . . . . . . . . . .100 pphm, 50% extension, no cracks
Electrical resistance . . . . . . . . . . . . . . . . . Greater than 10 mega ohms
Burst pressures
at ambient . . . . . . . . . . . . . . . . . . . . . .800 psi at 73 Deg F
at 180 Deg F . . . . . . . . . . . . . . . . . . . .600 psi at 180 Deg F
Thermal conductivity . . . . . . . . . . . . . . . .0.17 Btu/hr-ft-Deg F
Onix (EPDM) Properties
I.D. Onix Bend PEX Bend
Size
Radius Radius
3/8” . . . . . . .3” . . . . . . . . . . . .4
1/2” . . . . . . .4” . . . . . . . . . . . .5”
5/8” . . . . . . .5” . . . . . . . . . . . .6”
3/4” . . . . . . .6” . . . . . . . . . . . .7”
1” . . . . . . . .8” . . . . . . . . . . .10”
R4"
R3"
8"6"
4"
R3"
R4"
R3"
8"6"
4"
R3"
Onix Bend Radius PEX Bend Radius
&
FACT
D
ATA
SHEET
WattsRadiant Literature, May 1, 2003 ©WattsRadiant 2003 page 6
2.Onix cannot be permanently
kinked, eliminating wasted jobsite
time spent repairing kinks in PEX
tubing.
3.Onix is UV resistant for a minimum
of 5 years, so it can be left in the
sun on the jobsite without damag-
ing the tubing or the oxygen barrier.
4.Onix remains flexible to sub-zero
temperatures, making it easy to
install in frigid environments.
5.Onix has a burst rating of 600 psig
at 180°F, while PEX has a burst
rating of 325psig at 180°F, meaning
it will hold up to extreme "run-
away" boiler conditions.
6.Onix does not require special tools
to make the connection at the mani-
fold, saving hundreds of dollars in
tool costs.
7.Onix's oxygen barrier is inside the
tubing
, protecting it from job site
abuse.
8.Onix's outer cover is extremely
durable, protecting the inner tubing
and oxygen barrier from job site
abuse.
9.Onix is crush-resistant
, recovering
its shape after being compressed by
vehicles.
The Bottom Line
Onix Staple-Up is a very straightfor-
ward, simple-to-install system that is
easily understood by the installer and
the owner. The system doesn't require
special fasteners, metal plates, propri-
etary tools, heavy concrete, or a special
mechanical room design. It's a system
that works without all the complica-
tions.
Onix Staple-Up works, and it works
well. Try it on your next project. Design
the system with our Radiant Works soft-
ware and you'll have the experience of
22 years of successful radiant system
design guaranteeing it will work like a
champ!
Onix allows for a faster, easier, cleaner installation.
/
